Using LiPc, oxygen tension and oxygen consumption will be measured in hearts that are normally perfused and then subjected to cycles of ischemia. These data will be used to determine the capillary density of the beating heart myocardium. The effect of variation of blood flow, end diastolic pressure, blood oxygen saturation, and oxygen consumption, pressors, inotropes, vasodilators, and anti-anginal agents will be correlated with the capillary density.